The present invention relates generally to electroactive polymer systems and methods that convert between electrical energy and mechanical energy. More particularly, the present invention relates to electroactive polymers, transducers and devices having multiple active areas that communicate electrical energy between them. The present invention also relates to methods of using electroactive polymers having multiple active areas.
In many applications, it is desirable to convert between electrical energy and mechanical energy. Exemplary applications requiring conversion from electrical to mechanical energy include robotics, pumps, speakers, sensors, microfluidics, shoes, general automation, disk drives, and prosthetic devices. These applications include one or more transducers that convert electrical energy into mechanical work—on a macroscopic or microscopic level. Common actuator technologies, such as electromagnetic motors and solenoids, are not suitable for many applications, e.g., when the required device size is small (e.g., micro or mesoscale machines) or the weight or complexity must be minimized. Exemplary applications requiring conversion from mechanical to electrical energy include sensors and generators. These applications include one or more generators that convert mechanical energy into electrical energy. Common electric generator technologies, such as electromagnetic generators, are not suitable for many of these applications, e.g., when the required device size is small (e.g., in a person's shoe). These transducer technologies are also not ideal when a large number of devices must be integrated into a single structure or under various performance conditions such as when high power density output is required at relatively low frequencies.
Several ‘smart materials’ have been used to convert between electrical and mechanical energy with limited success. These smart materials include piezoelectric ceramics, shape memory alloys and magnetostrictive materials. However, each smart material has a number of limitations that prevent its broad usage. Certain piezoelectric ceramics, such as lead zirconium titanate (PZT), have been used to convert electrical to mechanical energy. While having suitable efficiency for a few applications, these piezoelectric ceramics are typically limited to a strain below about 1.6 percent and are often not suitable for applications requiring greater strains than this. In addition, the high density of these materials often eliminates them from applications requiring low weight. Irradiated polyvinylidene fluoride (PVDF) with various co-polymers is an electroactive polymer reported to have a strain of up to 4 percent when converting from electrical to mechanical energy. Similar to the piezoelectric ceramics, PVDF is often not suitable for applications requiring strains greater than 4 percent. Shape memory alloys, such as nitinol, are capable of large strains and force outputs. These shape memory alloys have been limited from broad use due to unacceptable energy efficiency, poor response time and prohibitive cost.
Typically, the above transducer technologies comprise a single active area for converting between mechanical and electrical energy; and a transducer is therefor dedicated to a single function. For a mechanical output application for example, a single piezoelectric ceramic is employed for actuation only. Alternatively, a single piezoelectric ceramic is typically configured solely for sensing in a sensing application. In many applications however, more advanced devices that convert between electrical and mechanical energy may be desirable.